1. Field of the Invention
This invention relates generally to semiconductor processing, and more particularly to apparatus and methods of packaging semiconductor chips.
2. Description of the Related Art
Heat is an enemy of most electronic devices. Integrated circuits, such as various types of processors, can be particularly susceptible to heat-related performance problems or device failure. Over the years, the problem of cooling integrated circuits has been tackled in a variety of ways. For conventional plastic or ceramic packaged integrated circuits, cooling fans, heat fins and even liquid cooling systems have been used, often with great success.
In the past few years, the size and power consumption of integrated circuits has climbed to the point where designers have turned to other ways to shed heat. One of these techniques involves using a metal lid for an integrated circuit package. The goal is to use the high thermal conductivity of the metal lid to ferry heat away from an integrated circuit. Of course, to ensure a conductive heat transfer pathway from the integrated circuit, designers early on placed a thermal paste between the integrated circuit and the lid.
One type of conventionally-used thermal interface material consists of a polymer, such as silicone rubber, mixed with thermally conductive metal particles, such as copper or aluminum. The polymer provides a compliant film between the integrated circuit and the overlying lid and easily provides a matrix to hold the thermally conductive metal particles. The thermal resistance of the thermal interface material is dependent on, among various things, the spacing between the metallic particles.
As noted above, heat sinks or fins are now routinely used to convey heat from chip packages. Heat sinks are usually connected to the package lid by some form of clamping mechanism or by way of one or more screws. A difficulty associated with the installation of heat sinks is the frequent lack of precision on the part of the installer. If the installation is done improperly, the heat sink may impose an asymmetric top-down loading on the lid. The asymmetric loading may cause the lid to rotate. If the rotation is severe enough, one side or the other of the thermal interface material may be stretched. The stretching, if severe enough may cause fracture or debonding of the thermal interface material. Even without mechanical failure, the stretching will increase the distances between the metallic particles in the polymer and thereby increase the thermal resistance thereof. Higher thermal resistance can lead to hot spots.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.